This invention relates to the field of subsurface valves for controlling flow of fluid through the bore of well conduit.
My copending application for a "WELL TOOL", Ser. No. 214,734, discloses a subsurface safety valve for blocking flow of fluid through a production string at a subsurface location by utilizing the well surface controls to effect a sequence of well pressure changes to operate the valve. That invention performed a valuable service but provided no means for preventing flow through the string or conduit when the surface control equipment was destroyed, damaged, or otherwise rendered inoperable before shutting in the well. Prior subsurface safety valves for controlling a full bore flow in a well, resulting from the destruction of the surface controls and the like, have been unreliable in wells having high allowable production rates due to the relatively small well pressure difference between normal well-flowing pressure and full bore well-flowing pressure.
An object of the present invention is to provide a new and improved well tool.
Another object of the present invention is to provide a new and improved subsurface safety valve operable by changes in the well pressure.